This invention relates to an improved high performance, broad application wheel in general. In particular, this invention relates to an improved high performance, broad application wheel for bicycles.
The search for better performance is endemic in every industry and the industry concerning the creation of high performance wheels is no exception. In particular, in the bicycle industry, a parade of innovations has seemingly addressed every aspect of wheel design. For example, Lipeles, U.S. Pat. No. 5,549,360 discloses a minimum weight wheel rim; Enders, U.S. Pat. No. 5,540,485 discloses a composite bicycle wheel having opposing spokes radiating from a central hub. Various other spoke wheel apparatus and methods for creating composite spoke wheels are set forth in U.S. Pat. Nos. 5,246,275; 5,184,874, 5,104,199; 5,061,013; 4,995,675; 4,930,844; and 4,930,843, for example. Without exception, prior art wheels have two common features. The first common feature in prior art wheels is that the rim depth is universally constant. The second universal feature of prior art wheels is that the spokes have a constant, cross-sectional shape.
A significant portion of the aerodynamic drag of a bicycle and rider in motion is created by the wheels. This problem has long been recognized and has been the subject of significant technical investigation and improvement. The drag associated with the wheel can be divided into two parts: spoke drag and rim drag.
Traditional tension wire spoke wheel designs optimized for minimum aerodynamic drag generally have an aerodynamically contoured rim and as few spokes as possible. The number of spokes is limited by the structure requirements of the tension wheel design. To further decrease the spoke drag, these spokes are often of a non-circular (elliptical) constant cross-section with the exception of the circular region retained for attachment of the spoke ends. Rim drag is minimized by use of an aerodynamically contoured rim with different designs utilizing depths of from 2 to 5 tire diameters; however, the depth is universally constant with any given prior art design.
Modern "aero" wheels utilize a reduced number (3, 4, or 5) of non-tension spokes. These spokes are capable of sustaining both bending and compression loads in addition to tensile loads. The larger cross-sections of these spokes are generally an aerodynamic contour of constant form and proportion. Some wheels have been fabricated using varying proportions of a constant formed spoke from the hub to the rim. The rim sections incorporated in these rims are of constant aerodynamic cross-section. While different designs utilize depths of from 2 to 5 tire diameters, the depth is universally constant within any given design.
The designs of all of these wheels attempt to obtain maximum performance for a given rider's capabilities. Directly measurable parameters of this performance include apparent and rotational drag, cross wind drag, rotational moment of inertia, and mass. Less tangible performance parameters of any given design are the comfort and feel of the wheel.
The inventors have determined that the local velocity profiles for a rotating wheel contain a significant region of flow reversal relative to the intended flow direction over the spokes. Additionally, the inventors determined that the sharp, trailing edge of conventional prior art designs produces separation and increased drag in this region of reverse flow. These effects are most pronounced in the presence of cross winds.
A drawback to the wheels known in the art is that solid disc wheels with no spokes are aerodynamically and structurally sound, but offer unacceptable wind resistance when cross wind exists. In circumstances where cross wind does exist, the wheel of choice, therefore, is a spoked wheel. Prior art wheels with spokes, however, have not provided a spoked wheel that is aerodynamically efficient in a head wind as well as a cross wind. Thus, there is a need in the art for providing a high performance, broad application wheel that performs as equally well in heads winds as in cross winds. It, therefore, is an object of this invention to provide an improved high performance, broad application wheel for providing optimum performance in any wind condition, including head winds and cross winds.